It is known that in automatic transmissions of vehicles, for example, a transmission filter is used on the inlet side of the transmission hydraulic pump. The transmission filter, typically a fine mesh screen or similar filtering media, prevents harmful contaminants from entering the hydraulic system where they can increase wear and cause scoring and sticking of hydraulic control valves. If a major part fails inside the transmission, the transmission filter may prevent pieces of that part from contributing to a more catastrophic transmission failure. Normally, transmission filters trap metal chips from parts such as gears and bushings and the normal fine material that results from wear of the hydraulic clutch facings and bands.
The known transmission filters are typically made of a plastic material formed as a frame around a mesh screen—the plastic frame molded into the desired configuration and onto the mesh screen. A rubber seal may be added to or molded with the frame. The rubber seal is used to seal the filter onto the inlet side of the hydraulic pump.
The known transmission filters, however, are currently manufactured using techniques that have certain drawbacks. For example, the molded plastic frame that forms the perimeter or outer edge of the filter also forms individual, smaller sections or windows within the frame. The mesh screen extends across some or all of the smaller sections or windows, creating individual filter sections. Depending on the application, a filter may have one or more individual sections or windows within the filter, with each section having a unique shape and configuration. As a result, the filter must be molded to form each of these individual sections or windows. During the molding process, the plastic material that forms the frame of the filter is typically injection molded in the desired configuration and molded at an elevated temperature over the screen sections. At this elevated temperature, the plastic material that forms the frame and individual sections may change shape and consequently may stretch the mesh screen material that extends across the individual section, sometimes to the point of tearing or ripping of the mesh screen material. In other applications, where a rubber seal is added to the filter, a liquid injection molding process is used where the rubber seal is pressed or squeezed onto the filter frame at an elevated temperature. In these applications, the elevated temperature and the pressing of the rubber seal causes the plastic material that forms the frame to expand or change shape resulting in the stretching of the mesh screen, again sometimes to the point of tearing or ripping of the mesh screen.
The present invention is directed at overcoming the known problem of tearing or ripping of the mesh screen as well as other known drawbacks with respect to the manufacture of filters and more broadly the application of molded plastic onto a mesh screen material.